1. Field of the Invention
The present invention relates to a keyhole for a main switch of a motorcycle.
2. Description of Related Art
Some keyholes for main switches for motorcycles are of a type in which a shutter plate is mounted for preventing permeation of dust and/or rainwater into the keyhole. Such a keyhole-shutter structure has been disclosed, for example in Japanese Utility Model Laid-open No. Sho 55-128847 entitled "Waterproof Structure for Cylinder Lock." As shown in FIG. 2 of this document, the keyhole-shutter structure is intended to bias a waterproof cover 6, which is mounted in a housing groove 1b of an inner cylinder 1, by a spring 7 to block a keyhole.
A shutter structure, substantially the same as the above structure, will be described in detail with reference to FIGS. 4 to 6(a)-6(c).
FIG. 4 is a perspective view of a front portion of a motorcycle. Referring to FIG. 4, there is shown a motorcycle 100 in which a fuel tank 101 and an engine 102 are provided on the central portion of a body frame (not shown). A front fork 104 is steerably mounted on a steering head 103 on the front side. A front wheel 105 is mounted on the lower ends of the front fork 104 and a handlebar 106 is mounted to the upper ends of the front fork 104. Two grips 107 are provided at the both ends of the handlebar 106. Two meters 108 and a main switch 109 are provided at the central portion of the handlebar 106. A clutch lever 111 and an exhaust pipe 112 are mounted on the motorcycle 100.
FIG. 5 is an exploded perspective view of a related art keyhole-shutter structure.
A keyhole-shutter structure 115 for mounting at the entrance end of a main switch 109 (see FIG. 4) includes a cylindrical protector block 120. In the upper portion of the protector block 120 is formed an approximately square recess 121. The bottom of the recess 121 is taken as a receiving plane 122, and a shutter plate 123 is fitted in the recess 121 in such a manner as to be slidable on the receiving plate 122. A cap 124 is positioned on the protector block 120. A compression spring 125 is provided for pushing the shutter plate 123 in the direction in which the shutter plate 123 is closed. Keyholes 126, 127 are positioned adjacent to the shutter plate 123 and in the cap 124, respectively. Locking claws 128 are mounted on the cap 124. A notch 129 is formed in the shutter plate 123.
FIGS. 6(a) to 6(c) are views showing the function and a problem of the related art keyhole-shutter structure.
A state in which the shutter plate 123 is closed is shown in FIG. 6(a). With the key not inserted in the keyhole, the shutter plate 123 is disposed to the left and is closed by a pushing force of the compression spring 125 to block the keyhole 126. In this state, there is no fear of permeation of dust and/or rainwater into the keyhole 126.
The key (not shown), when inserted from the top downwardly in the keyhole, pushes the notch 129. This allows the shutter plate 123 to move in the opening direction.
FIG. 6(b) shows a state in which the shutter plate 123 is opened.
When the key 130 is pulled upwardly, the shutter plate 123 is returned to the original state shown by FIG. 6(a).
The problem of the related art keyhole-shutter structure will be described with reference to FIG. 6(c). For example, the following problem may be encountered in parking the motorcycle having the related art keyhole-shutter structure. When the central portion of the shutter plate 123 is erroneously pushed at a pressure more than a specific value by a projection such as a different key 131, there is a possibility that the shutter plate 123 is not smoothly opened and is plastically deformed in the axial direction of the keyhole. In this case, if the deformed amount yl of the shutter plate 123 becomes larger, the shutter plate 123 may interfere with the receiving plane 122, thereby making the sliding movement of the shutter plate 123 difficult. Thereafter, it is difficult to insert the key in the keyhole, which degrades the operating feeling upon the release of a handle lock or upon the starting of the engine.